1. Field of the Invention
This invention relates to a digital data reproducing apparatus, and more particularly to an improvement of a digital data reproducing apparatus for reproducing digital data by means of partial response.
2. Description of the Related Art
In an optical magnetic disc device or the like, when recording data in digital, a partial response class 1 is often applied because optical disc apparatuses having an optical magnetic device can reproduce DC signals.
In the above apparatuses, the data recorded by means of the partial response system is reproduced. The reproduced signal is then decoded with reference to a specified threshold level.
In the optical disc, the DC level fluctuates due to double refraction on the disc surface, or the like. Further, in recording and reproducing, if the conditions of laser power etc., are different, the level of the reproducing signal fluctuates, and as a result, the suitable threshold level changes.